1. Field of the Invention
This invention relates to missile guidance systems. More specifically, this invention relates to improvements in the tracking and guidance of line-of-sight commanded missiles.
While the present invention is described herein with reference to particular embodiments and applications, it is to be understood that the invention is not limited thereto. Modifications may be made within the teachings of this invention without departing from the true spirit and scope thereof.
2. Description of the Prior Art
A typical line-of-sight guided missile system includes a launcher and a guided missile. The launcher typically includes a gunner's optical sight and an electronic guidance computer which automatically sends steering commands to the missile in flight. After launch, a beacon in the tail of the missile is activated and subsequently detected by a sensor on the launcher. The sensor is boresighted with the gunner's telescope and allows the operator to track the missile along its flight path. The sensor and associated processing circuit measures the angle between the missile and the gunner's line-of-sight. These displacements are transformed by computer into guidance commands which are sent to the missile over the command link. The gunner need only keep the cross-hairs of the sight on the target during missile flight.
This system is effective under conditions in which the target is visible to the gunner. Its operability is limited as to targets which are obscured by darkness, smoke, haze or conditions of poor atmospheric visibility. When the system is augmented by forward-looking infrared (FLIR) sensor and display, the operator has the capability of seeing many targets which would be otherwise obscured.
The following patents are illustrative of the prior art systems described above:
Pat. No. Patentee Issue Date 3,711,046 Barhydt et al January 16, 1973 3,761,180 Maxwell, Jr. et al September 25, 1973 3,820,742 Watkins June 28, 1974 3,998,406 Smith et al December 21, 1976 4,027,837 Miller, Jr. et al June 7, 1977 4,047,678 Miller, Jr. et al September 13, 1977
These systems typically utilize a source of infrared radiation (i.e., xenon flare or gallium arsenide diode) as a beacon mounted on the aft end of the missile. Some of these references provide for modulation of the beacon. A beacon signature which is modulated can be extracted from clutter at longer ranges than the same unmodulated beacon. If the beacon is a laser, the range performance of the system is further enhanced. As compared to conventional sources of infrared radiation, laser beacons have greater smoke, haze, fog and darkness penetration capability. In addition, a laser beacon can be electrically modulated at a very high frequency to provide enhanced counter measure resistance. Prior art systems often require a mechanical modulation mechanism. Such systems may be so heavy as to impair the performance of the missile by decreasing its range and/or responsiveness.